We previously isolated a novel autosomal recessive mouse mutation which we call wrinkle free (wrfr). wrfr mice are born with taut, shiny skin, a thickened epidermis, and a defective skin barrier. The mice die during their first day of life because their skin is so tight they are unable to breathe or suckle. There are also joint and facial defects that are likely secondary to the taut skin. We found by positional cloning that Slc27a4, the gene which encodes fatty acid transport protein 4 (FATP4), is mutated in wrfr-/- mice. FATP4 increases uptake of long and very long chain fatty acids by promoting their esterification to CoA via acyl-CoA synthetase activity. FATP4 is widely expressed and has been hypothesized to be important for intestinal uptake of dietary fatty acids. Our preliminary data show that the wrfr defect stems directly from the lack of FATP4 in the developing skin, and that the absence of FATP4 causes increased proliferation suprabasally, as well as widespread alterations in keratinocyte gene expression. Analysis of these changes suggests a premature activation of the keratinocyte differentiation program that is responsible for barrier formation during fetal maturation, yet the barrier is defective. FATP4-mediated events thus represent an important unexplored pathway regulating keratinocyte proliferation and differentiation. We hypothesize that the lack of FATP4 and the associated acyl-CoA synthetase activity leads to an alteration in lipid profiles that initiates a cascade of abnormal keratinocyte gene expression that contributes to the wrfr phenotype. We also hypothesize that FATP4 has later spatially and temporally distinct roles in lipid trafficking and metabolism that are required for barrier formation and sebaceous gland structure and function. To test these hypotheses, we propose to use new and existing FATP transgenic mice, mass spectrometric analysis of lipids, ultrastructural analysis of lamellar bodies and lamellar bilayers, analysis of sebum function and composition, and grafting of wrfr mutant skin to nude mice. With these approaches, we will determine the function of FATP4 in the skin and define novel mechanisms whereby lipids influence keratinocyte proliferation and differentiation. A number of human genetic skin diseases have been shown to stem from defects in genes that encode proteins involved in lipid trafficking. FATP4 clearly plays an important role in development of skin and appendages. A better understanding of how FATP4 functions in mice will lead to an overall better understanding of how lipid trafficking is involved in normal development of human skin and its barrier and appendages. PROJECT NARRATIVE (RELEVANCE): A number of human genetic skin diseases have been shown to stem from defects in genes that encode proteins involved in lipid trafficking. FATP4 clearly plays an important role in development of skin and appendages. A better understanding of how FATP4 functions in mice will lead to an overall better understanding of how lipid trafficking is involved in normal development of human skin and its barrier and appendages.